Gratings can be formed in optical fibers as taught by B. S. Kawaski et al, Optics Letters, Vol. 3, No. 2, August 1978, incorporated herein by reference and A Process Of Fabricating A Portion Of An Optical Fiber Capable Of Reflecting Predetermined Wavelength Bands Of Light by Donald C. Schmadel, Jr., said application filed concurrently herewith and completely incorporated herein by reference and assigned U.S. application Ser. No. 546,608, filed Oct. 28, 1983 (now abandoned). Grated optical fibers can be used as Bragg reflectors. When coupled in pairs, grated fibers can be used as interferometers to detect pressure changes in an undersea environment or down a wellbore.
The gratings are extremely fragile and reduce the mechanical strength of the fiber. Therefore, the fibers must be encased, i.e., ruggedized, as taught in A Ruggedized Grated Optical Fiber by Donald C. Schmadel, Jr. and Jack E. Goodman, filed concurrently herewith and completely incorporated herein by reference and assigned U.S. application Ser. No. 546,609, filed Oct. 28, 1983 (U.S. Pat. No. 4,593,969).
Forming gratings on such a small object is not an exact process. However, it is necessary that gratings be capable of reflecting very specific and narrow wavelength bands of light for most commercial applications. Thus, it would be desirable to be able to tune a fiber which reflects at a non-desirable wavelength so that it reflects light at a desired wavelength. The ability to tune the fiber would cut down on the cost required to manufacture exact reflective gratings and the need to throw away improperly fabricated gratings.